A useful configuration for vacuum coating apparatus includes a plurality of substrate-carriers arranged around the periphery of a rotatable cylinder or drum. Material is deposited on the substrates from elongated linear deposition sources, preferably sputtering cathodes, arranged adjacent the drum.
In one convenient arrangement, the drum may be contained, vertically oriented, in a box-type vacuum chamber having linear dimensions not significantly greater than the diameter and height of the drum. A linear magnetron sputtering cathode may be located in each corner of the chamber. Each cathode may be used to deposit a different material for depositing multilayer devices. Alternatively, one or more cathodes may be used to deposit the same material for the purpose of increasing deposition rate of that material on the substrates.
The above discussed drum-type coating apparatus has numerous advantages over more conventional coating apparatus wherein substrates are arranged on a horizontally oriented rotatable disc, or a series of discs rotatable in a planetary fashion.
The drum-type coating apparatus allows a large area of substrate to be coated in a relatively small chamber. The drum-type coating apparatus allows a very high degree of layer thickness uniformity to be achieved. Layers are deposited by multiple passes of substrates past the deposition sources. By depositing two materials, each from a different source, a mixture of the two materials may be effectively deposited.
In certain aspects, a drum-type coating apparatus has the advantages of an in-line type coating apparatus. A particular advantage is that linear magnetron sputtering sources may be effectively used as deposition sources, as they are, almost universally, in in-line sputtering apparatus. Linear magnetrons provide excellent deposition uniformity, and they may be operated for periods of days without maintenance. A linear magnetron equipped, drum-type coating apparatus may be though of, in effect, as a "cylindrical in-line" coating apparatus.
A particular disadvantage of the drum-type coating apparatus, however, is that it is not readily arranged as a load-lock type apparatus. In a load-lock coating apparatus, a coating chamber is held permanently (at least between maintenance intervals) under vacuum, and substrates are passed into and out of the chamber via exhaustable vacuum locks connected by a valve to the coating chamber. A load-lock type apparatus has an advantage that lengthy time periods are not required for exhausting and venting the chamber between coating cycles. Further, maintenance of the coating chamber under vacuum provides for reduced cosmetic defects in coated substrates. Such defects may be numerous in a coating apparatus in which the coating chamber is constantly vented and exhausted, thereby stirring up particulate matter which accumulates in the chamber between maintenance periods.
In in-line coating apparatus, a single flat substrate-carrier holds substrates to be coated. The flat nature of the substrate allows it to be passed conveniently through slit valves or locks into and out of a coating chamber. In-line apparatus has been used effectively for providing relatively sophisticated coatings at low cost. Achieving this low cost requires that a substantial area of a single layer system be produced. As such, apparatus is effectively used for providing architectural coatings.
In a revolving horizontal disc type coating apparatus, substrates may be essentially dropped through a valve or lock onto the disc for coating. In a revolving disc type apparatus the area of substrate which can be coated in a single charge is relatively limited. Because of this, a coating produced in such apparatus may be up to two orders of magnitude more expensive the same coating produced (volume considerations aside) in an architectural-scale in-line coating apparatus.
A load-lock, cylindrical in-line coating apparatus would be particularly useful for providing relatively low cost coatings without a requirement for architectural-scale product areas to achieve the relatively low cost. By way of example, one particular area in which such apparatus may be usefully applied, is in providing anti-reflection coatings for eye-glass lenses. The cost of such coatings is presently such that it is prohibitive for a majority of spectacle wearers.
The load-lock configurations presently used for disc-type or for in-line coating apparatus are not convenient in a drum-type coating apparatus. Dropping a substrate through a vacuum lock onto a drum is clearly not practical. Passing an entire drum loaded with substrates through a lock, would require a vacuum valve having dimensions greater than the drum. As a common drum dimension in drum-type coating apparatus may be between about 0.8 and 1.2 meters (m) in diameter and height, a vacuum valve (a gate-type valve) having an aperture of at least about 1.0 m would be required to accommodate passage of the drum. While construction of such a valve would not be impossible, it would certainly be a complex and expensive task. The cost of such a specially constructed valve would probably dominate the cost of constructing such apparatus. Further, a preferred apparatus would include separate load and unload-locks. This would necessitate two such expensive valves.
Providing a load-lock cylindrical coating apparatus requires a new and different approach to loading and unloading substrates into the apparatus through vacuum locks.